Not a teacher!
Hi there! I would say (b).
Non of your business means that you won't tell him or her your opinion because it is a private matter.
Your question should be: What do you think about the film (we've watched)?
I guess when you have just watched a film and you ask for it you needn't
especially mention that you mean that particular one....
In this forum we have many very qualified and professional teachers. Wait for them and their answers. As I am a student myself - don't trust me
Student or Learner